The problem of container deformation in response to pressure differences existing between the inside of a container, which is sealed to prevent leakage of any fluid contents, and the ambient atmospheric pressure, is well known in the packaging industry. Such container deformation may for certain container materials, especially some plastics, be non-recoverable.
Thin-walled, partially flexible containers which are often made of plastic material are particularly subject to the problem.
If the pressure in the container is higher than that of the ambient atmospheric pressure the container will tend to bulge, and may split or in extreme circumstances explode. If the pressure in the container is lower than that of the ambient atmospheric pressure the container wild tend to sag or be subject to inward collapse, this effect sometimes being referred to as `panelling`. The problem is most noticeably visible for essentially cylindrical containers.
The existence of pressure differences between the inside of a container having fluid contents and the ambient environmental pressure may also lead to mess when dispensing the contents. Where there is a positive pressure inside the container which rapidly equilibrates with the ambient on opening of the container, the fluid contents may spurt out causing unwelcome mess, or a possible safety hazard if product is spurted into the eyes of the opener.
There are a number of possible factors which may lead to the existence of the afore-mentioned pressure differences. The liquid contents of the container may, for example, be inherently chemically unstable or may be subject to reaction with any headspace gases in the container, or alternatively, in certain specific circumstances, may react with the container material itself. Any chemical reactions involving the liquid contents may lead to either production of gases, and hence to overpressure in the container, or to the absorption of any headspace gases thereby causing underpressure in the container.
Examples of liquid products which may react such as to generate pressure inside a container would include those products containing bleach components, Examples of liquid products which may be subject to reaction with headspace gases, particularly oxygen, such as to generate negative pressure inside a container include liquid detergent products, such as light duty liquid detergents, especially those containing certain perfume components,
The problem of container deformation as a result of chemical reactions involving the contents may, where the reaction is photolytically activated, be mitigated by making the container out of an opaque material. Opaque containers are however often perceived by consumers as being less aesthetically pleasing, and do not afford the possibility of being able to see clearly how much product remains in a partially filled container.
The Applicants have discovered that it is often red light (of approximately 410-500 nm wavelength) which photolytically activates the reaction of many perfume components commonly employed in detergent products. Where this is the case these unwelcome reactions of the perfumes can be mitigated by constructing the container out of a material capable of absorbing red light.
Storage of the container and contents at a low temperature may slow any chemical reaction processes. Cold storage may however, for reasons detailed below, tend to cause container deformation.
Pressure differences between the inside container pressure and ambient atmospheric pressure may also occur due to variations between container filling and storage temperatures. For example, the contents of the container may be added to the container at a temperature significantly different from the ambient environmental temperature, with the temperature of the contents being allowed to equilibrate to the ambient temperature whilst in the sealed container. Alternatively, the container may, for example, be filled with product at the ambient temperature of a typical factory working environment (say, 18.degree.-22.degree. C.) but then be stored in a cold warehouse, or be transported to be sold in an equatorial geography where typical daytime temperatures exceed 30.degree.-35.degree. C.
Pressure differences between the inside container pressure and ambient atmospheric pressure may even occur due to differences in the local ambient atmospheric pressure on filling and the local ambient atmospheric of the geographic location to which the product is transported.
Whilst the problem of container deformation as described above is most commonly found for essentially filled or partially filled containers, where the possibility of contents chemical instability is a particular source of the problem, the Applicants have also observed the problem to occur with empty containers, and particularly with empty sealed plastic bottles.
The problem of container deformation is less apparent in thick-walled containers which are by their nature less deformable. Consideration of cost and the desire to minimise usage of material resources, thereby reducing environmental impact, however, tends to favour use of thin-walled containers where possible.
Containers for many consumer products include devices for dispensing product in response to compression of the container by the user. Such containers, which would include for example squeezy plastic dishwashing or multi-purpose household cleaner liquid bottles, are by their nature made of flexible material to allow for compression, but are thus also inherently subject to deformation in response to other external factors.
Solutions to the problem of container deformation in response to differences between internal container pressure and external ambient pressure have been proposed in the art. Proposed solutions have included designing containers of specific shapes whereby the shape of the container has optimal resistance to deformation. This type of solution has the drawback that it limits the flexibility in designing such containers.
Other proposed solutions to the specific problem of build-up of overpressure in the container have included various valve systems. Further proposed solutions relate to various venting caps for containers which allow pressure generated inside the container to be released by escape of gas. U.S. Pat. No 3,315,831, U.S. Pat. No. 3,315,832, GB-A-2,032,892 and FR-A-1,490,177 for example disclose venting caps including composite cap liners. Co-pending European Application No. 92202223.1 discloses a venting and dispensing cap which allows for the dispensing of any liquid contents without the cap having to be removed from the container.
U.S. Pat. No. 3,471,051 describes a self-venting closure for containers including a composite venting liner composed of an asbestos-fiber lining material which is at least partly faced with a fibrous, spun-bonded sheet material.
FR-A-2,259,026 describes a venting closure including a gas-permeable venting liner comprised of polytetrafluorethylene material.
U.S. Pat. No. 4,136,796 describes a venting closure for a container including a membrane which is porous to gas under pressure wherein the membrane is formed from a cloth fabricated from fluorocarbon filaments. De-A-2,509,258 describes a pressure compensation screw cap including a venting seal made from fine cotton fabric impregnated with the polymer of a fluorinated or chlorinated hydrocarbon.
The Applicants have now discovered a sealing and venting system which provides a distinct solution to the afore-mentioned problem. The Applicant's sealing and venting system consists of a perforated area on to which is applied an essentially fluid-impermeable but gas-permeable membrane such as to provide a liquid/fluid leak tight seal under normal usage conditions which however allows venting of gases both in to and out of the container in response to small pressure differences. The membrane is treated to reduce its surface energy. The membrane is preferably formed from a synthetic material. The Applicant's sealing and venting system provides for rapid response to both underpressure and overpressure inside the sealed container, thus essentially preventing the container deformation problem.
The Applicant's distinct solution does not require the use of valves or venting caps of the type known in the art, which are often quite complex and can require expensive manufacturing. The Applicant's solution, unlike the valve systems known in the art, allows for two-way venting in response to relatively small pressure differences.
Co-pending European Application No. 92870173.9 discloses a plastic material which is impermeable to liquids, but permeable to gases. It is also disclosed that containers suitable for containing liquids which generate pressure inside a closed container can be made from said material. There is no disclosure in this co-pending Application of a sealing and venting system consisting of a perforated area in combination with a membrane of fluid-impermeable but gas-permeable material applied to the perforated area. The current invention provides the advantage that only a membrane of the fluid-impermeable but gas-permeable material is required, whilst the rest of the container may be made from conventional, cheaper materials.